The present invention relates to an improvement in an electromagnetic pump of a type used for fuel supply in a vehicle.
A simple electromagnetic pump has been desired as a vehicle fuel supply pump which allows easy machining and assembly of the constituting parts and provides stable pumping. Conventional electromagnetic pumps have both advantages and disadvantages and fail to satisfy all the needs described above.
In a conventional electromagnetic pump of this type, a sleeve member is fitted in a cylindrical housing, and a plunger is slidably fitted in the sleeve member. Suction and delivery chambers are formed at the two ends of the sleeve member. An electrical chamber having an excitation coil, a transistor, a printed circuit board, and the like is formed at the center of the sleeve chamber. Thus, the typical conventional electromagnetic pump is of a cylindrical type. In order to simplify the structure of an electromagnetic pump, electromagnetic pumps of a rectangular type are described in Japanese Utility Model Publication Nos. 56-42755 and 57-50542. wherein a sleeve member housing a plunger is disposed in a pump housing formed of a combination of U-shaped housing members. An excitation coil and the like are arranged in the housing.
However, according to the conventional electromagnetic pumps having the structures described above, the number of components is large, and machining and assembly are time-consuming and cumbersome. As a result, a compact, lightweight, low-cost electromagnetic pump cannot be provided.
In the conventional electromagnetic pump described above, a transistor arranged in the electrical chamber is normally fixed by screws or rivets on a heat sink through an insulating mica plate. The resultant assembly is further fixed by rivets on a printed circuit board or other yoke members. With this arrangement, mounting operation is time-consuming and cumbersome. A space for various electronic components mounted on the printed circuit board is limited, so that a sufficient insulating implementation must be provided, thus degrading the operation efficiency. Furthermore, since fastening members such as screws are used for the printed circuit board in the housing, if the printed circuit board is simply housed in the housing, electronic components may be brought into contact with a conductive member, resulting in a short circuit. Therefore, the structure with screws or the like is impractical. In such a structure, excessive stress occurs in each component when the component is mounted on a printed circuit board. The stress may cause the damage to the electronic components. The number of constituting parts is large, many assembly steps are required, and the electromagnetic pump has a large overall size. Furthermore, in order to improve waterproofing, an insulating coating is formed at the junction of the housing members, and a foamed member is filled in the interior of the housing.
Electromagnetic pumps of this type have been mounted in small vehicles with a stroke volume of 1,000 cc, so that a demand has arisen for a compact, lightweight, low-cost pump. No conventional electromagnetic pumps can answer the needs described above and much room is left for implementation to satisfy such requirements.